High-speed roll-up doors and driven belt conveyor systems are ubiquitous in industrial buildings, warehouses, and facilities throughout the world.
High-speed industrial roll-up doors employing an extendible and retractable curtain are used, for example, to cover doorways separating areas of a warehouse to contain conditioned air and to minimize air migration between the separated areas. In typical use, the curtain, comprising a heavy, durable, flexible material, such as a plastic, rubber, woven, or composite sheet material, is quickly retracted upwardly onto a rotating tube positioned above the doorway opening upon detection of an approaching vehicle (e.g., a forklift) or object to allow passage of the vehicle through the doorway, and is quickly extended downwardly from the tube (by rotating the tube in the opposite direction) to cover the doorway once the vehicle or object has passed. Thus, the doorway remains normally closed, covered by the curtain, and is opened for only short periods of time, to minimize migration of air between the areas separated by the curtain.
Drive systems for rotating the tube used to retract and extend the roll-up door's curtain typically employ a three-phase induction motor having an internal rotor shaft, with a transmission coupling the rotor shaft to the tube, the transmission comprising gears to regulate the speed of rotations and an electro-mechanical brake or clutch to regulate and/or decouple the tube.
Industrial conveyor systems similarly use a rotating tube or drum in frictional engagement with a continuous loop of heavy, durable, flexible material to convey items during the manufacture, packaging, or transport of items, for example, in in a warehouse. Typical conveyor systems drive systems are essentially identical to high-speed roll-up door drive systems—but oriented horizontally rather than vertically—using a rotating tube to convey the continuous loop of curtain-like material. Similar to known high speed door systems, known conveyor systems use a three-phase induction motor having an internal rotor shaft, with an attached transmission and an electro-mechanical brake or clutch coupling the internal rotor shaft to the tube.
While widely used, conventional three-phase motor drive systems, and motors having internal rotor shafts, suffer from numerous deficiencies. Induction motors are slow in both starting and stopping, such that startup torque is delayed past the initial application of power to the motor, stopping the motor likewise requires the assistance of a brake, such as an electro mechanical brake, or a clutch is used to decouple the motor shaft and/or transmission from the tube. Thus, near-instantaneous reversal of the motor direction is impossible, with the relatively long ramp-up and ramp-down times limiting the speed at which motor direction changes can be achieved.
Furthermore, the transmission and brake mechanisms required for use with the motors are themselves each comprised of a multitude of individual parts, such as gears, shafts, etc., all of which have wear surfaces and all of which require nearly continuous maintenance, such as maintaining lubrication and monitoring for wear, particularly in applications involving high-frequency cycling of one-hundred or more times per hour as is commonly incurred in operating industrial roll-up doors and conveyors.
Induction motors are also subject to overheating thus an additional cooling fan component is often added to the motor to direct cooling air through the motor during its operation. However, because the fan operates only via operation of the motor itself, cooling air is directed only while the motor is in operation. Once the motor stops, so does the flow of cooling air. Thus, in high-frequency operation, the flow of cooling air is intermittent and during the non-operational times the heat generated by the motor propagates to adjacent parts, raising the overall temperature of the entire system and driving up the internal temperature of the motor during each cycle of operation. The use of variable frequency induction motors further compounds the problem as the reduced shaft speed associated with those motors translates to a reduced volume of cooling air provided by the fan.
Thus, it can be seen that there is a need in the art for an improved drive system for use in high-frequency and intermittent industrial applications, such as high-speed roll-up doors and conveyor systems.